Method of making fiberscopes



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United States Patent 3,383,192 METHOD OF MAKING FIBERSCOPES Walter P.Siegmund, Woodstock, Conn., assignor to American Optical Company,Southbridge, Mass., a voluntary association of Massachusetts Filed Apr.13, 1964, Ser. No. 359,068 Claims. (Cl. 65-4) ABSTRACT OF THE DISCLOSUREThe method of making a flexible fiberscope including thejsteps ofassembling a plurality of preformed hoops of convoluted flexible opticalfibers in stacked relationship with each other throughout a relativelyshort length of each, adhesively securing the fibers together throughoutapproximately one-half of said length with a permanent bonding materialand throughout the other half of sail length with a temporary burnablebonding material, severing the assembly transaxially between saidbonding materials to form opposite ends of the fiberscope and heatingthe resulting temporarily bonded end to a tempera ture sufiicient toburn away the bonding material and effect fusion of the fibers.

This invention relates to optical image transfer devices formed of agreat number of relatively long and thin individually flexiblelight-conducting fibers having corresponding opposite ends thereofsecured together in such pre-arranged side-by-side relationship as tocompositely form image-receiving and emitting faces at opposite extemities of the devices. Such devices are known as flexible fiberscopesand the invention relates to constructional improvements therein andparticularly to a method of making the same.

In the manufacture of flexible fiberscopes, it has been the practice toconnect corresponding opposite ends of the optical fibers togethereither by fusion or cementing. In fused fiber optical bundles, imagequality in terms of appearance is generally higher than in cementedbundles due to the absence of the spacing between fibers which isprevalent in cemented bundles. However, in view of the fact that fusingseriously reduces the mechanical strength and flexibility of the fibersin the region of transition between the fused and flexible zones of thebundle due at least in part to the fibers being heated to above theirannealing temperature without being fused together, it is necessary toreinforce that region. One approach to such reinforcement has been toimpregnate the transition region with a fluid epoxy resin which canthereafter be po1ymerized in place. In medical endoscopes having fusedopposite ends, as one example, such reinforcement produces theundesirable result of substantially increasing the length of rigidity atthe distal portion of the fiber bundle beyond the already rigidly fusedzone and where extreme flexibility is actually required.

It has been found that at the image-receiving or distal end of afiberscope, lost image information and localized image distortionsresulting from the use of cemented fiber bundles are relativelyinsignificant in well packed bundles. Thus, the present inventioncontemplates the formation of a fiberscope having a well packedcemented, rather than fused, distal end section to minimize the lengthof the rigid portion of the fiberscopes distal end. At the opposite endof the fiberscope, however, an image-receiving face formed of a cementedbundle of fiber ends is undesirable especial ly from the viewpoint ofappearance of an image presented 3,383,192 Patented May 14, 1968 "ice atsuch a face. This is due to the presence of cement and/ or voids betweenfibers.

Thus, at the proximal end of the fiberscope where added length ofrigidity is not of consequence, the present invention contemplatesfusing the fibers together to eliminate spacing therebetween with a viewto improving the appearance of images produced at that end of thefiberscope.

In view of the fact that fiberscopes are normally constructed of amultiplicity of individually extremely thin and flexible fibers usuallynumbering in the several thousands, each being of only a few thousandthsof an inch or considerably less in cross-sectional dimension, it will beappreciated as this description progresses that the fabrication of sucha device having one end section fused and the other cemented wouldordinarily be accompanied by serious if not unsurmountable problemssince, for achieving acceptable definition and resolution of image, thefibers must be arranged in substantially identical geometrical patternsat opposIte ends of the structure.

In accordance with principles of this invention, a simple, reliable andunique process is contemplated for manufacturing fiberscopes of theabove-mentioned character and it is, therefore, an object of theinvention to provide for maximum flexibility of the distalimage-receiving end of a fiberscope and, at the same time, to providefor maximum image quality, especially in terms of cosmetic appearance ofan image produced at the proximal end of the fiberscope where the extentof flexibility is of less consequence.

This objective and others which may become apparent hereinafter isachieved in the manner disclosed in the following detailed descriptionwhich is accompanied by a drawing in which:

FIG. 1 illustrates, in side elevation and partly in section, anexemplary fiberscope having lens-supporting end fittings thereon;

FIGS. 2, 3, 4 and 5 illustrate various steps performed in the process ofthe invention according to one aspect thereof;

FIG. 6 is an enlarged elevatio-nal view of the proximal orimage-receiving end face of a fiberscope formed in accordance withprinciples of the invention;

FIG. 7 is a view similar to FIG. 6 of the opposite or distalimage-receiving end face of the fiberscope; and

FIG. 8 is an enlarged longitudinal cross-section of the fiberscopehaving a section thereof broken away inter mediate its opposite ends.

Referring now to the drawing, there is shown in FIG. 1 exemplaryfiberscope 10 formed of a number of long and thin individually flexibleoptical fibers 12 bundled together in side-by-side relationship withcorresponding opposite ends thereof secured together to form at thedistal end of the fiberscope an image-receiving face 14 and at theproximal end thereof an image-emitting face 16. Fibers 12 areunconnected and free to flex individually intermediate opposlte endsections of fiberscope 10 so they are free to flex individually.

For purposes of illustration only, end fittings 18 and 20 supportingobjective and eye lenses 22 and 24 respectively are shown in simplifiedform as being fixedly connected to opposite ends of fiberscope 10. Itwill be understood that various, more elaborate, end fittings, lenssystems, and also enclosing outer sheaths or the like, not shown, wouldordinarily be applied to fiberscope 10 to equip same for use as amedical diagnostic instrument or the like.

The present invention relates more particularly to improvements inconstructional details of the fiber optical section of such aninstrument and, accordingly, fittings 18 and 20 are only illustrative ofthe many variations thereof well known in the art.

Briefly and in general, fiberscope 10 operates upon receiving a patternof image-forming light projected against face 14 by objective lens 22,to transfer by internal reflection elemental areas of the image patternthrough respective fibers receiving the same to face 16. At face 16, theimage pattern in mosaic form is viewed with the assistance of magnifyingeye lens 24. For some applications of use, however, neither of the endfittings 18 and 20 are required if, for example, an illuminated objectto be viewed is placed immediately adjacent to or against one face 14 or16 and the image thereof is viewed directly at the other face withoutthe aid of an eye lens. Thus, the term fiberscope when used herein isintended to refer more particularly to the structure of the bundle ofoptical fibers 12 without accessories such as fittings 18 or 20.

Fibers 12 each comprise one or more cores of light conducting materialof relatively high index of refraction each surrounded by a relativelythin cladding of ma terial of a lower index of refraction than the core.Fibers comprising the integral flexible structure of more than oneindividually clad core all fused together are commonly referred to asmultifibers and this invention relates to the fabrication of fiberscopesformed of either single core fibers or multifibers. The fibers of eithertype may, as one example, comprise cores of optical flint glass havingan index of refraction of approximately 1.62 each clad with a relativelythin layer of crown or soda-lime glass having an index of refraction ofapproximately 1.52..

Faces 14 and 16 of. fiberscope 10 are optically ground and polished torender respective fibers 12 individually highly receptive and conductiveto image-forming light presented upon the distal end face 14 andsimilarly con ductive and emissive to light presented to the proximalend face 16 by transference through the fibers. Proximal end face 16may, for some applications of use, be sand blasted, etched or otherwiserendered light-diffusing.

Referring now to details involving the fabrication of fiberscope 10, itwill be seen that it is formed with a relatively short portion ofcorresponding lengths of fibers 12 cemented together at distal endsection 26 (see FIGS. 1, 6, 7 and 8) while the proximal end section 28is fused together and reinforced in transition region 29 adjacent; thefused portion (see FIG. 8).

Fiberscope 10 is according to one aspect of the inven tion provided withidentically geometrically patterned end faces by first forming a numberof fiber hoops 30, one of which is shown separately in FIG. 2. Each hoop30 consists of a single fiber strand wound to a ribbon-like single ormultiple layer thickness of a widthv approxi mately equal to thatdesired of one transverse dimension of the fiberscope. The meancircumferential dimension of each hoop 30 is controlled to beapproximately equal to the length desired of fiberscope 10. In order toobtain. maximum precision in the geometrical identity of fibers atopposite ends of the ultimate fiberscope, hoops 30 should each be of asingle layer or one fiber thickness or, if multiple layer thicknessesare used, each layer should be wound in the same direction and at thesame helix angle as its predecessor.

Hoops 30, suflicient in number to provide an assembly of a thicknessapproximately equal to that desired. of fiberscope 10, are assembledtogether in stacked relation, one within. the other, substantially asshown in FIG. 3. As will become apparent hereinafter, opposite end facesof the fiberscope are formed by severing the stack of hoops 30transversely in a plane of demarcation. illustrated by line 32 (FIGS. 3and 4). For a. detailed description. of this general technique forforming flexible fiberscopes, reference may be had to Patent No.3,033,731 issued May 8, 1962, to Henry B. Cole and assigned to assigneeof the present application.

In accordance with one feature of the present invention, the convolutesof each hoop 30 are cemented together along a narrow transverse strip 34(see FIG. 2) preferably with a permanent bonding material such as, forexample, an epoxy resin of the two-stage curing type commonly referredto as a B-stage epoxy which, upon application in solution, contains asolvent adapted to dry .at normal room or slightly elevated temperaturesto render the resin adhesively varnish-like in consistency andsubsequently permanently hardenable when polymerized or cured by theapplication of heat in the order of approximately 250 Fahrenheit. Strip34 is of such controlled width as to extend along the length of hoop 30a distance no greater than that required for making a secure connectionof the distal ends of fibers 12 of fiberscope 10 so as to provide thedistal end of fiberscope 10 with the least possible amount of rigidity.By way of example, in fabricating a fiberscope intended to have across-sectional dimension of between three and four millimeters on aside, strip 34 should be approximately five millimeters in width or, fora six or seven millimeter square fiberscope, strip 34 should be seven oreight millimeters in width.

Immediately adjacent to strip 34 and preferably adjoining same along aline of demarcation 36, the convolutes are further cemented togetheralong another trans verse strip 38 of approximately the same width asstrip 34 but with a temporary removable bonding material or cement suchas cellulose nitrate in a solvent of nitromethane or the like all ofwhich can be subsequently burned away. Upon being so cemented, hoops 30are successively stacked one within the other or one upon the other, asthe case may be, to form the bundle illustrated in FIG. 3. Strips 34 and38 are arranged in accurately superimposed relationship so that the lineof demarcation 36 of each hoop 30 coincides with line 32 along which thebundle is to be subsequently severed.

The entire section of the bundle of hoops 30 including the zone thereofconnected together with the permanent bonding material and thatconnected together with the temporary bonding material is placed withindouble clamp 40 (FIG. 4) having slot 42 in which line 32 isapproximately centered. Sufficient clamping force is applied thereto byscrews 44 and 46 to compact the bundle and adhesively connect togetheradjoining respective strips 34 and 38. The different cements beingslightly tacky or cohesive under such clamping force. Alterna= tively, athin layer of the same cements used. to form strips 34 and 38respectively can be applied therebetween as the hoops are stacked toassure good adhesion of one to another. If such a connecting cement isused, however, it should be applied sparingly to prevent undue spacingof the fibers in adjoining hoops.

The epoxy-bonded zone or section 26 of the bundle of hoops in FIG. 4 isnext heated to a temperature suflicient to cure and fully set the epoxyresin and thus form a permanent bond between all fibers of all hoops 30in that section. This may be accomplished by applying heat to section40' of clamp 40.

In curing the B-stage epoxy resin which has been at least partiallydried at room temperature, heat of ap proximately Fahrenheit is appliedfor a period of time sufficient to melt and cause the resin to wetfibers 12 of the bundle. Thereafter, the temperature is raised toapproximately 250 Fahrenheit for a period of time sufficient to fullypolymerize the resin. and thereby effect permanent hardening thereof.Conduction of heat to section 40" of clamp 40 will not adversely affectsection 28 of the bundle of hoops since the maximum temperature used incuring the epoxy resin is well. below that which would adversely affectthe cement. used in section 28.

Having permanently bonded the fibers of hoops 30' together in section26, the bundle is sawn or otherwise severed along line 32 with suitablemeans such. as the circular cutter 48 shown partially broken. away inFIG. 4. The severance along line 32 separates the now permanently setepoxy-connected section 26 from. section 28 and thus forms substantiallygeometrically identical opposite end faces 14 and 16 of fiberscope 10.

Section 26, the end face 14 of which is illustrated in FIG. 7, isremoved from section 40* of clamp 40 and section 28 can then be heatedand fused in section 40" of the clamp or removed therefrom to otherholding or clamping means for fusing to form end face 16 shown in FIG.6.

In a presently preferred procedure, section 28 is placed in a relativelysnug fitting channeled support 50 of re fractory material which ishighly geometrically stable and relatively non-adherent to glass whensubjected to glass-fusing temperatures. Such a refractory material isdisclosed in Patents No. 2,440,187 and No. 2,764,491 assignee of thisapplication. A parting agent such as gold foil, not shown, can be usedto line the channel of support 50, if desired. Block 52, preferablyformed of the same material as support 50, is placed upon section 28 ofthe cemented fibers 12 to exert as a result of its weight a slightcompressing force tending to compact the bundle and effect secure fusionthereof.

Section 28 is heated by any suitable means such as electrical coils 54to a temperature of, for example, from 1250 F. to 1450 F. to causefusion of fibers 12 one to the other. During such heating, the cement ofstrips 38 is burned away and pressure applied by block 52 causes fibers12 to assume an interfitted fused relationship with out voidstherebetween substantially as illustrated in FIGS. 6 and 8. Theresultant fused section 28 is ann-ealed, thereafter cooled to roomtemperature and removed from support 50. The squeezing-together offibers 12 in support 50 and elimination of cement 38 will tend toshorten one transverse dimension of end face 16 slightly in thedirection of application of pressure and thus produce a slightanamorphism in images received at face 16. This, however, is notordinarily consequential. However, while not illustrated in the drawing,the invention also contemplates the use of other types of supports suchas one having two sides thereof movable in rightangular directionsrelative to one another toward the fiber bundle with pressure beingapplied equally to each during fusion. This will obviate imageanamorphosis in critical cases.

In view of the fact that fibers 12 are unavoidably heated totemperatures above annealing temperatures of their glasses in thetransition region 29 (FIG. 8) where these fibers are unconnected, theyinherently become relatively inflexible and fragile in that region. Thefragile region normally extends back from the fused section 28 adistance approximately equal to the length of the fused section itself.Thus, in order to avoid breakage of fiberscope 10 in this region duringuse thereof, fibers 12 are reinforced after fusion of section 28 byimpregnation with an epoxy resin 56 initially in liquid form and whichis cured to form a permanent bond with the fibers in the mannerdescribed above with relation to the similar curing of epoxy strips 34.

Accordingly, fiberscope 10 thus formed comprises a distal end section 26having fibers 12 secured together with a cement to provide for themaximum possible extent of flexibility of the distal portion of thefiberscope while at the opposite proximal end section 28 whereflexibility is not of consequence, fibers 12 are fused together toprovide for maximum quality in cosmetic appearance of images produced onface 16 at that end. At the same time, fibers 12 are substantiallyidentically geometrically arranged at opposite faces 14 and 16.

It should be understood that while, for purposes of clarity inillustration, fiberscope 10 has been shown to be comprised of only a fewrelatively large diameter fibers 12, it would in actuality embody agreat number of fibers each of an exceptionally small cross-sectionalsize.

I claim: 1. The method of making an image transfer device (10) of amultiplicity of bundled energy-conducting fibers (12) arranged incompact side-by-side relationship with each other throughout a sectionof the length of the bundle wherein the improvement comprises the stepsof connecting said fibers (12) together throughout one portion (26) ofsaid section with a substantially permanent bonding material (34) andthroughout another portion (28) of said section adjacent said oneportion with a removable bonding material (38), said materials beingdisposed in contiguous side-byside relationship with a plane ofdemarcation (32) therebetween extending transversely through the bundleat one side of which a face (14) is to be formed and at the other sideof which another face (16) is to be formed both on said bundle;

severing said bundle generally along said plane of. demarcation (32) toform said faces (14 and 16);

removing said removable material (38) from between lengths of saidfibers (12) in said other portion (28); and fusing said lengths of thefibers (12) together. 2. The method according to claim 1 wherein saidpermanent bonding material (34) and said removable bonding material (38are characterized in that they are respectively hardenable and removableupon application of heat thereto and said method further includes thesteps of applying heat to said permanent bonding material (34) of atemperature sufficient to harden same and removing said removablebonding material (38) by the application of heat of a temperaturesufficient to effect burning thereof.

3. The method according to claim 2 wherein removal of said removablebonding material (38) and fusion of adjacent portions of said fibers(12) are successively effected by the steps of heating same to atemperature sufiicient to burn said material (38) and raising thetemperature of such heat sufficiently to render said fibers (12) fusibleone to the other and compressing the bundle of fibers (12) during suchheating sufficiently to compact same without materially altering thegeometrical relationship thereof.

4. The method of making a flexible image transfer device of amultiplicity of lengths of energy-conducting fibers (12) arranged incompact side-by-side relationship with each other as a bundle having anumber of zones (26, 28) therealong wherein said fibers (12) arearranged in a cross-sectionally congruent relationship in one zone (26)with reference to another (28) wherein. the improvement comprises?connecting said fibers (12) together in one of said zones (26) with asubstantially permanent bonding material (34); v

connecting said fibers (12) together in anothe 'f of said zones (28)with a temporary bonding material (38) and maintaining the arrangementof said fibers (12) in said other zone (28) while removing saidtemporary bonding material (38); fusing said fibers (12) together insaid other zone (28); forming an optically finished face on one end ofeach of said zones extending transversely of said bundle;

impregnating a section of the length of said bundle adjacent to saidother zone (28) with a fluid but settable material (56); and

causing setting of said last-mentioned material (56). t

5. The method of forming a flexible image transfer device of amultiplicity of lengths of energy-conducting fibers (12) arranged incompact side-byside relationship with each other as a bundle having anumber of zones (26, 28) therealong wherein said fibers (12) are incrosssectional congruent relationship in one zone with reference toanother, the improvement comprising:

connecting said fibers together in said zones (26, 28)

with bonding material; forming a face extending transversely of saidbundle on one end of each zone; maintaining the arrangement of fibers(12) in one of said zones (28) while removing an amount of said bondingmaterial sufiicient to permit fusion of said fibers (12) one to theother in said one zone (28); fusing said fibers together in said onezone (28); impregnating a section of the length of said bundle adjacentto said one zone (28) with a fluid but.

settable material (56-); and causing setting of said material.

References Cited UNITED STATES PATENTS MacNeille. Cole Woodcock 65-4 XWoodcock. Siegmund.

